Process for the preparation of aryl-substituted normal paraffin hydrocarbons



Dec. 16. 1969 BERGER HE PREPARATION 0F ARYL-SUBSTITUTED NORMAL PARAFFIN ,HYDROKCARBONS Filedy Nov. 15. 1967 United States Patent O 3,484,497 PROCESS FOR THE PREPARATION OF ARYL-SUBSTITUTED NORMAL PAR- AFFIN HYDROCARBONS Charles V. Berger, Western Springs, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Nov. 15, 1967, Ser. No. 683,303 Int. Cl. C07c 3/52, 15/00 U.S. Cl. 260-'671 9 Claims ABSTRACT OF THE DISCLOSURE Concerns an improvement in a process for the preparation of aryl-substituted normal paraffin hydrocarbons. Process involves steps of: dehydrogenation of normal paraflns to normal mono-olelins, hydrogen separation, alkylation of monocyclic aromatics with resulting normal mono-olefms, separation of alkylation products and recycle of unreacted normal paralin to dehydrogenation step. Problem involves build-up of non-normal hydrocarbons in normal parain recycle stream causing dehydrogenation catalyst instability and deterioration in product quality. Solution embodied herein comprehends separating non-straight chain hydrocarbons from at least a portion of the recycled normal paraffin stream.

The subject of the present invention is an improvement in a process for the preparation of aryl-substituted normal parain hydrocarbons. More particularly, the present invention relates to an improvement in one of the commercially feasible routes to this type of arylalkane which route uses normal paraltins and mono-cyclic aromatics in conjunction With a selective catalytic dehydrogenation opertaion and an alkylation procedure. The improvement follows from my recognition of the detrimental eiects caused by the presence of non-normal hydrocarbons (especially cyclics) in the normal parain charge to the dehydrogenation step of the combination process Coupled with this recognition, was my observation that even where substantially pure normal paralins are charged to the combination process, economic and equilibrium factors dictate the recycle of unreacted normal paratlins to the dehydrogenation step. And a process operated with this type of recycle will inevitably tend to build a concentration of non-normal hydrocarbons in this recycle stream because of side-reactions such as skeletal isomerization, cyclization, cracking and alkylation of cracked products, etc., in the dehydrogenation zone that even the best of the available dehydrogenation catalyst cannot completely avoid. More to the point, these dehydrogenation catalysts can be designed to suppress undesired side-reactions that result in non-normal hydrocarbons, but as of yet no way has been found to completely eliminate them. Drawing upon the above analysis of the problems, the present invention provides a continuous procedure for the elimination of non-normal hydrocarbons from a side-stream taken from the paraflin recycle stream, thereby holding the concentration of nonnormal hydrocarbons in this parailin recycle stream at tolerable levels with corresponding increase in the stability characteristics of the dehydrogenation catalyst and in the quality of the arylalkane product.

One of the major problems prevalent in centers of population throughout the world is the disposal of sewage containing detergents in even small quantities. Such disposal problem is especially vexacious in the case of those detergents having an alkylaryl structure as the nuclear portion of the detergent molecule. These detergents produce stable foams in hard or soft waters in such large ICC quantities that the foam clogs sewage treatment facilities and often appears in sufcient concentration in such facilities to destroy the bacteria necessary for suicient biological action for proper sewage treatment. One of the principal offenders of this type of detergent is the alkylaryl sulfonates, which, unlike the fatty acid soaps, do not precipitate when mixed with hard water containing calcium or magnesium ions. And since these compounds are only partly biodegradable, the detergent persists in solution and is carried through the sewage treatment plant in substantially unchanged form. Having a tendency to foam, especially when mixed with aerating devices and stirrers, large quantities of this detergent are discharged from sewage digestion plants into rivers and streams where the continuing presence of the detergent is marked by large billows of foam on the surface of these streams. Other offenders of this type of detergent are the polyoxyalkylated alkyl phenols and the alkylphenol-polyoxyalkyated amines. These same synthetic detergents also interfere with the anaerobic process of degradation of other materials, such as grease, and thus compound further the pollution caused by sewage plant eluents containing such detergents. These dilute detergent solutions often enter subsurface water current which feed into underground water bodies from which many cities draw their water supply, and the alkylaryl-based detergents nd their way into the water supplies drawn from water-taps in homes, factories, hospitals, and schools.

It has been established that the biodegradability of the ultimate detergent product is determined by the arylalkyl compound that is used in the preparation of the detergent. And more particularly, it has been found that these detergents are more readily degrable by sewage bacteria if the long chain alkyl substitutent on the aromatic nucleus is of a simple, straight-chain configuration. In fact, the preferred intermediate from the biodegradability stand-point is an aryl-substiuted normal paraflin hydrocarbon. Consequently, there has been established a sub-` stantial requirement for this type of hydrocarbon. In view of the fact that this type of hydrocarbon is customarily prepared by an alkylation operation, it commonly is referred to in the art as a species of detergent alkylate or linear detergent alkylate, for example, linear alkylbenzene.

The linear detergent alkylate can be converted into a wide variety of detergents as is well-known to those skilled in the art. For example, the detergent alkylate may be sulfonated and thereafter neutralized with a suitable alkaline base, such as sodium hydroxide to form an alkylaryl sulfonate (anionic) type of detergent which is most widely used for household, commercial and industrial purposes. The detergent alkylate can also be converted to a non-ionic type of detergent by nitrating the alkylate to form a nuclearly mono-nitrated intermediate which on reduction yields the corresponding alkylarylamine. The amino radical is thereafter reacted with an alkylene oxide or an alkylene ep'ichlorohydrin to form an alkylaryl-polyoxyalkylated amine (containing from 4 to about 30 oxyalkylene units) which is a highly elfective detergent. Another large class of detergents prepared from detergent alkylate are the oxyalkylated phenol derivatives in which an alkylphenol base is prepared by alkylation of a phenol. Still other products having an alkylaryl base are Widely known in the arts, although alkylaryl sulfonates constitute the largest single class of surfactant products which are typically synthesized from this detergent alkylate.

Responsive to the demand for this linear detergent alkylate, the art has come up with a number 0f ways to use normal paralns as a source for the straight chain alkyl substituent on the aryl nucleus. One route to the detergent alkylate involves: selective catalytic dehydrogenation of the normal paraffins to the corresponding normal mono-olefin having the same number of carbon atoms followed by alkylation of an aromatic with the resultant normal mono-olefin using an acid-acting catalyst to yield an aryl-substituted normal paraffin hydrocarbon. The dehydrogenation step typically operates on normal paraffin hydrocarbons having about 9 to about 20 carbon atoms to produce a normal mono-olefin having the same number of carbon atoms. The alkylation step has a dual function: the first being the separation of the product olefin from the unreacted normal paraffins, and the second being the preparation of the desired arylalkyl hydrocarbon. In this process a dehydrogenation catalyst is preferably employed which has a high selectivity for the production of a normal mono-olefin with the complementary capability to suppress undesired side reactions such as skeletal isomerization, secondary dehydrogenation, cyclization, dehydrocyclization, polymerization, cracking, etc. In view of the fact that equilibrium considerations necessarily limit conversion levels in the dehydrogenation step, the economics d of the resulting process require that the unreacted normal paraffins be recovered from the mixture of reactants and products withdrawn from the dehydrogenation step and recycled to this step. For example, typical conversion levels efficiently attained in this dehydrogenation step with preferred catalyst are in the range of about to about by weight of the normal paraffin depending on temperature, catalyst life, etc. The preferred procedure is to allow the unreacted paraflins to pass through the alkylation zone (where they are substantially unchanged), and separate them from the products of the alkylation reactions by fractional distillation.

The problem of concern to the present invention stems for this necessity of recycling the unreacted parains to extinction. Despite the use of dehydrogenation catalysts having selectivities for the desired mono-olefin approaching 95% to 98%, I have now found that the small amounts of non-normal hydrocarobns for-med in the dehydrogenation step plus any non-normals present in the normal paraffin feed, accumulate in this recycle stream because they are relatively intractable at the conditions employed in the dehydrogenation step. Furthermore, I have found that these non-normal hydrocarbon adversely affect the stability of the dehydrogenation catalyst, and when the operating conditions in the dehydrogenation step are raised to compensate for their presence, product quality is adversely affected because these non-normal hydrocarbons are forced to undergo dehydrogenation and alkylation, thus damaging biodegradability and/or detergency of the final product. Consequently, the broad concept of the present invention involves the removal of non-normal hydrocarbons from the recycled paraffin stream of this process with resulting improvement in dehydrogenation catalyst stability and in the quality of the product alkylate.

It is, accordingly, one object of the present invention to provide an improvement in a process for the synthesis of aryl-substituted normal paraffin hydrocarbons utilizing normal paraffin hydrocarbons and mono-cyclic aromatic hydrocarbon. Another object is to improve the quality of the linear detergent alkylate produced by selective catalytic dehydrogenation of the normal paraffins to monoolefins followed by alkylation of the mono-olefins with an aromatic hydrocarbon. Still another object relates to a selective catalyst dehydrogenation operation wherein unreacted normal paraffins having 9 to 20 carbon atoms are recovered and recycled to extinction, the object being to improve the stability of the catalyst used therein.

In one embodiment, the present invention relates to an improvement in a process for the preparation of an arylsubstituted normal paraffin hydrocarbon utilizing a normal paraffin hydrocarbon and a mono-cyclic aromatic hydrocarbon. In this process a normal paraffin hydrocarbon and hydrogen are contacted with a dehydrogenation catalyst in a first conversion zone at conditions sufficient to form a normal mono-olefin having the same number of carbon atoms as the normal paraffin hydrocarbon with attendant formation of a minor amount of non-normal hydrocarbons. A mixture of hydrogen and hydrocarbons is Withdrawn from the first conversion zone and separated into a hydrogen-rich gaseous phase and a hydrocarbonrich liquid phase. The hydrocarbon-rich liquid phase and a mono-cyclic aromatic hydrocarbon are contacted in a second conversion zone with an alkylation catalyst at conditions sufficient to form arylalkyl compounds. A mixture of hydrocarbons is withdrawn from this second conversion zone and separated, in a fractination system, into a mono-cyclic aromatic-rich fraction, a normal paraffinrich fraction containing non-normal hydrocarbons, .and an aryl-substituted normal paraffin fraction. The normal paran-rich fraction is recycled to the first conversion zone in order to supply a portion of the normal paraffin hydrocarbon thereto, and because it contains non-normal hydrocarbons the stability of the dehydrogenation catalyst is adversely affected, and the quality of the aryl-substituted normal paraffin fraction ultimately deteriorates. In this process, the improvement of the present invention comprises: removing non-normal hydrocarbons from at leaSt a portion of the recycled normal paraffin-rich fraction thereby increasing the stability of the dehydrogenation catalyst and improving the quality of aryl-substituted normal paraffin hydrocarbon fraction obtained from this process.

In another embodiment, the process of the present invention relates to an improvement in a process for the preparation of an aryl-substituted normal paraffin hydrocarbon utilizing a hydrocarbon distillate boiling in the kerosine range and a mono-cyclic aromatic hydrocarbon. In this process, the hydrocarbon distillate containing normal paraffin hydrocarbons and non-normal hydrocarbons is initially subjected to a separation operation effecting the removal of non-normal hydrocarbons therefrom. The resulting stream of normal paraffin hydrocarbons is commingled with a recycle stream containing normal paraffin hydrocarbons, and the resulting mixture and hydrogen are contacted with a dehydrogenation catalyst in a first conversion zone at conditions sufficient to form a normal mono-olefin having the same number of carbon atoms as the normal paraffin hydrocarbon with attendant formation of non-normal hydrocarbons. A mixture of hydrogen and hydrocarbons is withdrawn from the first conversion zone and separated into a hydrogen-rich gaseous phase and a hydrocarbon-rich liquid phase. The hydrocarbonrich liquid phase and a mono-cyclic aromatic hydrocarbon are contacted in a second conversion zone with an alkylation catalyst at conditions sufficient to form arylalkyl compounds. A mixture of hydrocarbon is withdrawn from the second conversion zone and separated, in a fractionation system, into a mono-cyclic aromatic-rich fraction, a norm-al paraffin-rich fraction containing non-normal hydrocarbons, and an aryl-substituted normal paraffin fraction. The normal paraffin-rich fraction is recycled to the rst conversion zone, and because it contains non-normal hydrocarbons, the stability of the dehydrogenation catalyst is adversely affected and the quality of the aryl-substituted normal paraffin fraction ultimately deteriorates. In this process, the improvement of the present invention cornprises withdrawing a side-stream from the recycled normal paraffin-rich fraction and passing this side-stream back to the initial separation step of the process, thereby effecting the removal of non-normal hydrocarbons from this portion of the paraffin recycle stream with resulting increase in the stability of the dehydrogenation catalyst used in the rst conversion zone and in the quality of the arylsubstituted normal paraffin hydrocarbon fraction recovered from this process.

Other embodiments and objects of the present invention encompass further details about: the hydrocarbon distillate, normal paratiins and mono-cyclic aromatics which can be charged thereto, the types of catalysts used in the conversion zone thereof, the process conditions used in each step thereof, the mechanics of the conversion, se'paration, and product recovery steps employed therein, etc. These embodiments and objects will be hereinafter described in the detailed discussion of the various elements of the present invention.

Before proceeding to a detailed discussion of the elements of the present invention, it is necessary to define certain terms and phrases used herein. The phrase arylsubstituted normal parain hydrocarbon denotes a secondary aryl-substituted alkane having two straight-chain alkyl groups on the resulting tri-substituted carbon atom attached to the aryl nucleus; for example:

where R1 and R2 are norma-l alkyl groups. The phrase normal or straight-chain hydrocarbons refers to hydrocarbons having their carbon atoms linked in a continuous chain. The phrase liquid hourly space velocity is to be construed to refer to the volume of the stated lluid as a liquid charged to the reference zone per hour divided `by the volume of the zone cont-aining catalyst.

With respect to the embodiment of the present invention where the charge stock is a normal parain, suitable charge stocks are normal paraftins having at least 9 carbon atoms and especially 9 to about 20 carbon atoms. Representative members of this class are: nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, and mixtures thereof. Of particular significance to the present invention are normal parains of about 9 to about 15 carbon atoms since these produce mono-olens Which can be utilized to make detergents having superior biodegradability and dctergency. For example, a mixture containing a four or five homologue spread such as C10 to C13, C11 to C14, or C11 to C15 provide an excellent charge stock. Moreover, it is preferred that the amount of non-normal hydrocarbons present in this normal paraffin stream be kept at low levels. Thus it is preferred that this stream contain greater than 90 Wt. percent normal paraffin hydrocarbons, with best results achieved at purities in the range of 96 to 98 wt. percent or more. It is within the scope of the present invention to pretreat the normal paraffin charge stock by any suitable means for removing aromatic compounds; for example, by contacting it with an aqueous solution of sulfuric acid.

In the embodiment of the present invention in which the charge stock is a hydrocarbon distillate, any suitable source for the hydrocarbon distillate can be used provided normal parains having 9 to 20 carbon atoms are contained therein. This class includes, for example, an appropriately boiling fraction of the straight run petroleum distillate, or of the products of a Fischer-Tropsch reaction which includes parafiin hydrocarbons in the C9 to C211 range, or of the hydrogenation products of ethylene polymerization which includes parafns having from 9 to about carbon atoms, and of the hydrogenated fatty acids which upon complete reduction produce paraffinic hydrocarbons having straight-chain configurations. The most widely available and generally preferred source of normal parailins in the C9 to C211 range is a kerosine fraction boiling within the range of about 300 F. to about 500 F., and more preferably the fraction thereof boiling from about 350 F. to about 450 F. In general, when hydrocarbon distillates are charged to the present invention, it is preferred that the fraction be pretreated in any suitable hydrogen treating operation for the substantial removal of sulfurous and nitrogenous compounds with attendant saturation of olenic compounds. Thus, the hydrocarbon distillate charged to separation system of the present invention will preferably be substantially saturated and substantially nitrogen and sulfur free.

Suitable catalysts for use in the dehydrogenation step of the present invention generally comprises one or more metallic components selected from Groups VI and VIII of the Periodic Table and compounds thereof. Such catalysts are generally composited with a carrier material which consists of one or more refractory inorganic oxides selected from the group of alumina, silica, zirconia, magnesia, and the like refractory oxides. It is particularly important that the catalyst employed in the dehydrogenation zone does not promote isomerization of the normal paraflins or of the resultant olefinic product. Accordingly, the catalyst utilized is preferably made nonacidic by compositing it with one or more alkali metals, or alkaline earth metals, or compounds thereof. Furthermore, the conversion to the desired mono-olefin is enhanced when the noble metals of Group VIII are employed with platinum being particularly preferred.

Insofar as degree of conversion and avoidance of side reactions is concerned, a particularly preferred catalyst for the dehydrogenation step comprises: an alumina component; a platinum-group metallic component; and alkali or alkaline earth metal component or compounds thereof; and a component selected from the group consisting of arsenic, bismuth, antimony, sulfur, selenium, tellurium, and compounds thereof.

The alumina component of this preferred dehydrogenation catalyst generally has an apparent bulk density less than about 0.50 gram/cc. with a lower limit of about 0.15 gram/cc. The surface area characteristics are such that the average pore diameter is about 20 to about 300 angstroms; the pore volume is about 0.10 to about 1.0 milliliter per gram; and the surface area is about 100 to about 700 square meters per gram. It may be manufactured by any suitable method including the well-known alumina sphere manufacturing procedure detailed in U.S. Patent No. 2,620,314.

The alkali component of this preferred dehydrogenation catalyst is selected from both alkali metals-cesium, rubidium, potassium, sodium and lithium-and the alkaline earth metalscalcium, magnesium, and strontium with lithium being preferred. It is present in an amount, based on the elemental metal, less than about 5% by weight of the total composite with a value in the range of 0.01% to about 1.5% generally being most preferred. In addition, the alkali component may be added to the alumina in any suitable manner, especially in an aqueous impregnation solution thereof, and thus suitable cornpounds are the chlorides, sulfates, nitrates, acetates, carbonates, etc., such as lithium nitrate. It may be added either before or after the other components are added, or during alumina formation-for example, to the alumina hydrosol before the alumina carrier material is formed.

The platinum group metallic component is generally selected from the group of palladium, iridium, ruthenium, rhodium, osmium, and platinumwith platinum giving best results. It is used in a concentration, calculated as an elemental metal, of about 0.05% to about 5.0% by weight of the catalytic composite. This component may be composited in any suitable manner with impregnation by a water soluble compound, such as chloroplatinic acid, being especially preferred.

The fourth component of this preferred dehydrogenation catalyst is selected from the group consisting of arsenic, antimony, bismuth, sulfur, selenium, tellurium, and compounds thereof. Arsenic is particularly preferred. This component is typically used in an amount of about 0.01% to about 1.0% by weight of the final composite. This component is preferably present in an atomic ratio to the Group VIII metallic component of from about 0.1 to about 0.8. Intermediate concentrations are preferably employed such that the atomic ratio is about 0.2 to about 0.5. This component can be composited in any suitable mannera particularly preferred way being via a water soluble impregnation solution such as arsenic pentoxide, etc.

This preferred catalytic composite is thereafter typically subjected to conventional drying and calcination treatments at temperatures in the range of 800 F. to about 1100J F. Additional details as to the preferred dehydrogenation catalyst for use in the present invention are given in the teachings of U.S. Patent No. 3,291,755 and 3,310,599 issued to Vladimir Haensel et al.

Any suitable alkylation catalyst may be utilized in the alkylation step of the present invention. Representative of these are: sulfuric acid of about 85% concentration and preferably higher; substantially anhydrous hydrogen fluoride, generally not containing more than 10% water; anhydrous aluminum chloride or aluminum bromide, preferably in the presence of the corresponding hydrogen halide; boron trifluoride either with or without addition of hydrogen fluoride, and either as such or adsorbed on a solid support, such as a boron trifiuoride-modied inorganic base; phosphoric acid which is generally deposited on a carrier material such as kieselguhr, hydrated silica, etc.; and the like. The preferred catalyst for the present invention is anhydrous hydrogen fluoride of from about 90% concentration or higher; another preferred catalyst is the previously mentioned boron triiluoride.

Details as to concentration, method of use, etc. of these preferred alkylation catalysts will `be found in the teachings of U.S. Patent No. 3,249,650 insofar as the hydrogen uoride catalyst is concerned, and in the teachings of U.S. Patent No. 3,200,163 'for the boron triuoride catalyst.

Having characterized the catalysts used in the dehydrogenation step and the alkylation step of the present invention and the charge stocks used therein, reference is now had to the attached drawing for the detailed explanation of the flow schemes, process conditions, and operating parameters employed in the two principal embodiments of the present invention. The attached drawing is merely intended as a general representation of the ow schemes employed in the embodiments of the present invention with no intent to give details about heaters, condensors, pumps, compressors, valves, process control equipment, etc., except where a knowledge of these devices is essential to an understanding of the present invention or would not be self-evident to one skilled in the art. Moreover, in view of the fact that the present invention involves a combination process no attempt is made in this drawing to represent details about the specifics of each of the process steps except Where detailed information is essential for a proper understanding of the invention.

Referring now to the drawing and considering first the embodiment of the present invention in which the charge stock is a substantially pure normal paran stream, valve 21 in 19 is closed and valve 2 in line 1 is open. For the sake of illustration, it is assumed that the substantially pure normal parain stream comprises 99% by weight normal tetradecane. This tetracane stream enters the process via line 1, is commingled with a recycle tetradecane stream at the junction of line 1 with line 14, and the resulting combined .paraflin stream passed into dehydrogenation zone 20. Also charged to zone 20 is a hydrogen recycle stream entering through line 5; it contains substantially pure hydrogen and is passed thereto in an amount of about 1 to about 20 moles of hydrogen per mole of parain entering the zone, and preferably about 5 to about 15 moles per mole of normal paraffin.

In some cases, it is advantageous to use a di'luent such as steam, methane, carbon dioxide, benzene, etc., in one or more of the streams entering zone 20 in order to control heat of reaction therein, or to adjust the partial pressure of one or more of the reactants charged thereto, or to activate the catalyst used therein. For example, a preferred procedure with the hereinabove characterized -preferred dehydrogenation catalyst is to saturate at least a portion of the entering hydrogen stream with Water prior to its introduction into zone 20.

yIn any event, zone 20 contains a fixed bed of the preferred dehydrogenation catalyst which in this case cornprises about 0.75% by weight platinum, about 0.50% by weight of lithium, combined with an alumina carrier material consisting of A inch spheres and having about 0.3 atom of arsenic for each atoms of platinum. The hydrogen and normal paran stream entering dehydrogenation zone 20 may be admixed prior to their entrance into this zone or shortly thereafter. In addition, both of these streams are heated by heating means, not shown in the attached drawing, to the desired conversion temperature which for the preferred dehydrogenation catalyst ranges from about 750 F. to about 1100 F. and preferably about 800 F. to about 1000 F. Similarly, the ypressure within dehydrogenation zone 20 is maintained within the range of about 10 p.s.i.g. to about 100 p.s.i.g. with best results obtained in the range of 15.0 to about 40 p.s.i.g. Likewise, a liquid hourly space velocity based on the combined paraflin stream of from about 10.0 to about 40.0 is utilized in this dehydrogenation zone.

The function of dehydrogenation zone 20 is to selectively convert the normal paraffin charged thereto to normal mono-olelins having the same number of carbon atoms. Although the preferred class of catalyst is capable of accomplishing this conversion at selectivities as high as to 98%, there is, unfortunatey, stilll a minor amount of side products concurrently formed. For the case where the charge is normal tetradecane, the principal product is normal tetradecane and the side products are typically C14 conjugated dienes, C14 isomers, naphthenes, aromatics, lower molecular Weight paraffins and olefins, etc.

A mixture of hydrogen and hydrocarbons is withdrawn from zone 20 via line 3 and passed through condensing means, not illustrated, in which the temperature of the mixture is lowered to a value of about F. The resulting cooled mixture is then introduced in separation zone 4. In separation zone 4 a hydrogen-rich gaseous phase separates from a hydrocarbon-rich liquid phase. The hydrogen-rich gaseous phase is withdrawn from zone 4 via line 5 and recycled through compressive means not shown to supply hydrogen to dehydrogenation zone 20. In addition, excess hydrogen is withdrawn through line 22 during the operation of the process in order to maintain pressure control with zone 20` Similarly, line 22 may be used during start-up operations to inject hydrogen into the hydrogen loop.

The hydrocarbon-rich liquid phase is Withdrawn from separation zone 4 and passed via line 6 to alkylation zone 7. In general, it is preferred to subject this stream prior to its passage into zone 7, to a suitable operation designed to remove water, if such has been added to the charge to zone 20.

Also charged to alkylation zone 7 is a mono-cyclic aromatic which enters the process via line 13. Moreover, part of the source of the mono-cyclic aromatic may be a recycle stream, the origin of which will be hereinafter discussed. In general, any alkylation mono-cyclic aromatic may be used in the process of the present invention as long as it is separable from the normal parain stream by fractional distillation. Typical examples of this class are: benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene, phenol, mono-nitrobenzene, etc. The preferred mono-cyclic aromatic is benzene,

In alkylation zone 7, the aromatic compound and the hydrocarbon-rich liquid phase from separating zone 4 are contacted with the alkylation catalyst which is preferably a solution of hydrogen fluoride as previously explained. It is understood that these streams may be introduced simultaneously, or in admixture with each other, or the aromatic compound may be contacted with alkylation catalyst followed by the addition of the hydrocarbon-rich stream thereto. The mole ratio of aromatic compounds to the mono-olefin contained in the hydrocarbon stream is generally maintained above equimolecular ratios, preferably from about 2:1 to about 30:1 in order to minimize polyalkylation of the aromatic compounds and polymerization of the olefin.

In alkylation zone 7, the reactants are maintained in contact with the alkylation catalyst for a reaction period of about to 100 minutes, the exact contact time being dependent on a number of factors such as type of reactants and catalyst temperature, etc. The temperature maintained in this zone is within the range of about 0 F. to about 200 F. and preferably from about 70 F. to about 150l F. Likewise, pressure sufiicient to maintain the catalyst and reactants in liquid phase is generally employed.

Following the alkylation reaction a mixture of hydrocarbons comprising the products of the alkylation reaction in combination with unreacted hydrocarbons charged thereto, are withdrawn via line 8 and passed to fractionation system 9. In the preferred case in which the alkylation catalyst is a solution of hydrogen fluoride. The effinent from alkylation zone 7 is first passed to a separating zone in which an acid phase separates from a hydrocarbon phase. This hydrocarbon phase is then typically passed to a stripping column wherein it is stripped of hydrogen fluoride, and the resulting hydrogen uoride-free hydrocarbon phase is thereafter charged to fractionation system 9.

In general, fractionation system 9 can comprise any suitable train of fractionation columns designed to separate the hydrocarbon charged thereto into a mono-cyclic aromatic-rich fraction, a normal paraffin-rich fraction, an aryl-substituted normal paraffin fraction, and a heavy alkylate fraction. Preferably, the system comprises three fractionation columns, the first being designed to separate mono-cyclic aromatics from the hydrocarbons passed thereto. In a preferred case in which benzene has been alkylated, this column will be designed to separate excess benzene from the mixtures of hydrocarbons withdrawn from alkylation zone 7. The resulting recovered benzenerich fraction is then preferably recycled to the alkylation zone. The bottoms from this benzene column are then passed through treating means, not shown in the attached drawing, wherein alkyl liuorides are substantially removed-for example, by contacting with alumina treaters. The treated bottoms from the benzene column are then passed into a normal paraffin column wherein a normal paraffin-rich fraction, in this case principally a C14 fraction, is recovered as overhead and passed via line 14 back to dehydrogenation zone 20. The bottoms from the paraffin column are then passed to a detergent alkylate column wherein the detergent alkylate product is recovered as overhead with a minor amount of a heavy alkylate product, typically comprising diphenylalkanes, dialkylindanes, etc. being recovered as bottoms. This heavy alkylate is primarily a consequence of the dienes produced as a side product in zone 20.

Turning to a consideration of the normal parafiin recycled stream passing via line 14 back to dehydrogenation zone 20, I have now found that it contains straight-chain and cyclic isomers of the normal parain charged to the process. As previously explained, these generally are synthesized in the dehydrogenation zone and because they are somewhat refractory to the conditions employed in the dehydrogenation zone tend to accumulate in this paraffin recycle stream. Furthermore, I have found that these nonnormal hydrocarbons can cause rapid dehydrogenation catalyst deactivation if their concentration in this recycle stream exceeds about by weight. Hence, it is a feature of the present invention that the concentration of normal paraffins in the normal paraffin recycle stream is maintained at about 90 wt. percent and preferably about 95 wt. percent. Referring now to the drawing, this essential feature of the present invention is effected by withdrawing a side stream from the normal paraffin recycle stream via line 15 and charging the resultant side stream to separation system 16. At this point, it is to be noted that it is not, in general, necessary to treat the entire paraffin recycle stream since a small amount of non-normal hydrocarbons can be tolerated in the dehydrogenation zone, and it is only, therefore, necessary to remove nonnormal hydrocarbons from this recycle stream at about the same rate that they are formed in the dehydrogenation zone. Hence, only about 0.1 vol. percent to about 20 vol. percent of the recycle normal paraffin stream is withdrawn via line 15 and preferably about 0.2 vol. percent to about 5 vol. percent.

The function of separation system 16 is the separation and recovery of normal parains from hydrocarbon mixtures containing normal paraffins, isoparafns, and cyclic compounds. Separating agents which have the capacity to segregate compounds on this basis are well known to the art and are referred to as molecular sieves. The preferred `molecular sieves for this type of service are characterized as a dehydrated metal aluminosilicate having a zeolite structure in the crystals of aluminosilicate and containing pores of about 5 angstrom units in cross sectional diameter, which are of sufficient size to permit the entry of normal parainic compounds having four or more carbon atoms but are not of sufficient size to permit the entry of branch chain or cyclic compounds. The metal constituents of these zeolite composition is typically selected from the alkaline earth metals, preferably calcium or magnesium. These molecular sieves are typically prepared by interaction of silica, alumina, and an alkaline base and water to form a zeolitic, hydrous alkali metal aluminosilicate which precipitates from its aqueous solution as a mass of nely divided crystals. The recovered alkali metal derivative in the form of hydrated zeolite is thereafter typically ion-exchanged with an alkaline earth metal salt, and dehydrated via calcination to form the desired molecular sieve.

Separation system 16 may be operated according to swing-bed principles wherein two individual contacting columns each having separate inlet and outlet lines connected thereto are provided in one of which the extraction of normal paraffins is effected substantially at the same time that regeneration of the sieve particles and recovery of normal paraffins are effected in the other contacting column. In this mode of operation, the side stream from the paraffin recycle stream flows either upwardly or downwardly through a fixed bed of molecular sieve material wherein the relatively straight chain components enter the pore structure of the molecular sieve particles and are retained therein with the non-normal hydrocarbons passing through the bed. This operation is conducted at atmospheric pressure or higher and at temperatures of about 70 F. to about 300 F. or higher, depending upon the boiling point of the normal paratiin recycle stream, as they are preferably sufficient to maintain Substantially liquid phase in this contacting column. The bed of molecular sieves that is on the normal paraffin recovery portion of the cycle is contacted with a displacing Huidgenerally a normal paraffin of lower molecular weight than the normal parafiin hydrocarbon utilized in dehydrogenation zone 20 for example, normal butane or pentane-to effect displacement of the heavy normal paraflins from within the pores of the molecular sieves. The displaced heavy normal parafns ow out of the column and are passed typically to a fractionation column wherein any displacing uid is separated therefrom. The resultant substantially pure normal parain hydrocarbons are then passed to line 18 back into line 14 wherein they continue back to dehydrogenation zone 20.

In a preferred embodiment, the separation system employed in zone 16 continuously separates normal hydrocarbon from non-normal hydrocarbons in a simulated continuous operation according to the principles given in the teachings of U.S. Patent No. 3,310,486 issued to D. B. Broughton. In this system the molecular sieves are arranged in a series of extraction zones and by utilizing a complicated switching system, the countercurrent lio-W of molecular sieves relative to the stream to be purified is simulated. The key feature of this system involves a multibed system with constantly changing inlet and outlet ports so that the one portion of the system is constantly extracting normal paratlins at the saine time another portion of the system is being treated to recover normal paraflins. Consequently, the flow of Substantially pure normal paraflins from this system is essentially continuous. Reference may be had to the cited patent for additional details as to the exact procedures utilized in the operation of this rather sophisticated system.

Regardless of which procedure is utilized in separation system 16, a substantially pure normal paraliin bydrocarbon stream is Withdrawn therefrom and reintroduced into line 14 thereby lowering the concentration of non-normal hydrocarbons is the resulting total normal parafiin recycle stream passing via line 14 back to line 1 and into dehydro genation zone 20.

Considering now the embodiment of the present invention wherein the charge stock is a hydrocarbon distillate boiling in the kerosine range-preferably, a C12 to C14 fraction thereof-this hydrocarbon distillate is introduced into the system Via line 19 with valve 21 open and Valve 2 closed. The hydrocarbon distillate passes into separating system 16 wherein it is commingled with the side stream of normal parains entering separating system 16 via line 15. The resulting hydrocarbon mixture is then subjected in separating system 16 to a separation operation of the type hereinabove characterized, and preferably the separation operation described in U.S. Patent No. 3,310,486. As a result of this separation operation, the non-normal hydrocarbons contained in this hydrocarbon mixture are separated therefrom and passed out of separating system 16 via line 17. In this embodiment, the normal paraffin hydrocarbons recovered from this hydrocarbon mixture are injected into the normal paralin recycle stream at the point line 18 joins line 14. With the above exception, the operation of the other steps in this embodiment are substantially the same as hereinabove described and will not be repeated here.

In the case Where the hydrocarbon distillate entering the process through line 19 is subjected to a pretreatment with hydrogen in the presence of a suitable hydrotreating catalyst, it is within the scope of the present invention to pass the side stream from the normal paratlin recycle stream to this pretreatment step. ln fact, this is the preferred procedure when the alkylation catalyst used in Zone 7 is hydrogen fluoride, thereby providing an additional safeguard against the buildup of alkyl tluorides in the influent to dehydrogenation zone 20.

The following examples are introduced to illustrate further the novelty, mode of operation, and utility of the present invention. It is not intended to limit unduly the present invention since the examples are intended to be illustrative rather than restrictive.

EXAMPLE I This example shows the benefits of using the present invention by contrasting the results obtained with and without it for substantially the same charge stock catalyst and ovv scheme (given in the attached drawing).

The charge stock used in this example was a normal paraffin mixture containing: 0.3 wt, percent n4C10, 26.6 Wt. percent n-C11, 31.3 Wt. percent n-C12, 25.0 wt. percent n-C13, 13.2 Wt. percent n-C1.1, and 0.4 wt. percent n-C15. In addition, the charge stock contained a minor amount of mono-olefins, mono-cyclic paraflins, dioleiins, dicyclic paraffins, and aromatics. Moreover, the initial boiling point was 392 P. and the end boiling point Was 470 F.

The catalyst used in the dehydrogenation zone 20 was prepared according to the method given in U.S. Patent No, 3,291,755. Analysis of the catalyst showed that it contained 0.76 wt. percent platinum, 0.041 wt. percent arsenic, 0.55 wt. percent lithium, all composited with an alumina carrier material. Furthermore, it had an'ABD of 0.46, a surface area ot 145 m.2/g. and a pore volume of 0.40 mL/g. This catalyst was supported in zone 20` as a lixed bed Of 1/16 inch spheres.

The catalyst used in alkylation zone 7 was a solution of 95 wt. percent hydrogen fluoride.

In both runs dehydrogenation zone 20 was run with the objective of producing a 10 Wt, percent conversion to normal oleiins. Conditions used were a LHSV of about 28.0 luz-1: a hydrogen to hydrocarbon mole ratio of 9.0, a pressure at the outlet of Zone 20 of abut 30 p.s.i.g., and a temperature in the range of about 850 F. to 925 F. temperature being selected throughout the runs at a level suicient to sustain the desired conversion.

Alkylation zone 7 was run with a benzene charge stock at a mole ratio of benzene to total olen in the inliuent thereto of about l0, a volume ratio of hydrogen fluoride solution to inuent hydrocarbon of about 2, a temperature of about F. to about 140 F., and a residence time of about 20 minutes.

In the first run, the control run, no side stream was withdrawn via line 15 and the entire normal paraffin recycle stream was passed directly to zone 20. At the start of the recycle operation a reactor temperature of about 886 F. was necessary to sustain a 10% conversion in dehydrogenation Zone 20. In addition, the ei'lluent from zone 20 at the start of recycle of normal paraffin via line 14 contain about 3.7 Wt. percent non-normals. After about 27 barrels of charge per pound of catalyst contain in zone 20 had been processed, a temperature of about 900 F. was necessary to sustain the desired conversion level in zone 20, and more importantly the efliuent from this zone contained about 9.0 Wt. percent non-normals. Thus, these results evidence the sharp buildup of nonnormal hydrocarbons in the recycle stream to zone 20. In addition, the decline of activity of the catalyst is reectcd in the sharp temperature rise that was necessary to sustain the desired conversion level; it was at a rate of about 0.635 F./BPP which contrasts sharply with a rate of about 0.19 F./BPP for once-through operations.

The second run was made according to the present invention with a fresh load of catalyst, and about 2.0 to 2.5 vol. percent of the normal parain recycle stream was continuously withdrawn throughout this run via line 15, and replaced with an equal amount of a stream having the same composition as the charge stock.

At the beginning of the recycle operation, a temperature of about 886 F. was necessary to sustain conversion and the eifluent from the dehydrogenation zone contained about 3.1 wt. percent non-normals. After about 27 barrels of the charge stock per pound of catalyst in zone 20 had been processed, the comparable readings were a temperature of 893 F. and a wt. percent of non-normals of about 4.5%. This indicates a deactivation rate of about 0.258 F./BPP which compares quite favorably with the results for once-through operation.

Accordingly, the present invention produces a sharp increase in the stability of the catalyst employed in the dehydrogenation Zone.

EXAMPLE II This example illustrates the improvement of the present invention in the embodiment where a normal paraflin stream is charged thereto. Accordingly, the flow scheme used in this example is the same as that given in the attached drawing with valve 21 closed and valve 2 open.

The charge stock utilized in this example is a C10 to C14 normal parain-containing stream having an initial boiling point of 373 F. and an end boiling point of 437 F., and containing 6.4 wt. percent n-C111, 41.6 Wt. percent n-C11, 41.2 wt. percent n-C12, 8.7 wt. percent n-C13, and 0.4 wt. percent n-C1.1. Hence, this stream is 98.3 Wt. percent normal parafiin. The results of a mass spectometer analysis indicate the remaining material is primarily mono-olelins, diolelins, monocyclic parafns and dicyclic paratiins. Moreover, this charge stock contains 0.1 wt. ppm, of sulfur and 4.3 wt. ppm. of nitrogen.

The catalyst used in alkylation zone 7 is a solution of posite of: alumina with platinum, lithium, and arsenic. It is manufactured by the procedure given in U.S. Patent No. 3,291,755. A chemical analysis shows it to contain, by weight, 0.76% platinum, 0.074% arsenic, and 0.495% lithium, all calculated on an elemental basis. It is present in this zone in the form of a-xed bed of 1/13 inch in diameter spheres.

The catalyst used in alkylation zone 7 is a solution of substantially anhydrous 95 wt. percent hydrouoric acid.

In the first run, a control run in which lines and 18 are closed off, the charge stock enters the process via line 1, and is commingled with a recycle parain stream from line 14 in a ratio of about 6 volumes of recyclestream per volume of fresh charge stock. The resulting mixture of hydrocarbons is then joined with a recycle hydrogenrich stream provided inan amount sufficient to supply about 10 moles of H2 per mole of hydrocarbon contained in the mixture. The combined stream is then heated by suitable heating means to a temperature Within the range of 850 F, to about 950 F., with the exact selection within this range being continuously increased in order to sustain a conversion level of 10% by weight of normal parain entering zone 20. The resulting heated mixture of hydrocarbons and hydrogen is then passed in dehydrogenation zone containing the fixed bed of the dehydrogenation catalyst at a charge rate corresponding to a LHSV of about 30, based on the mixture charged. Zone 20 is operated at a pressure of about p.s.i.g.

The total eflluent from zone 20 is withdrawn via line 3, cooled to about 80 F., and passed into separation zone 4. A hydrogen-rich gaseous phase is withdrawn from zone 4 vial line 5 and a portion of it passed, through suitable compressing means, back to zone 20. A liquid hydrocarbon phase is withdrawn from zone 4 Via line 6, dried and introduced into alkylation zone 7.

In alkylation zone 7, the 'liquid hydrocarbon phase is admixed with benzene, entering alkylation zone 7 via line 13, in an amount of about l0 moles of benzene per mole of normal mono-olefin. The resultinghydrocarbon mixture is then admixed with anhydrous hydrogen fluoride in a ratio of about 2.0 volume of HF per volume of hydrocarbon mixture. Alkylation zone 7 is operated at a temperature of 100 F., a pressure of 250 p.s.i.g. and a residence time of about 20 minutes. Alkylation zone 7 is also provided with a suitable cooling means to remove the heat from the exothermic reaction taking place therein.

The alkylation zone eluent is then passed to a separating zone, not shown in the attached drawing, wherein an acid phase separates from a hydrocarbon phase. The acid phase is recycled within zone 7 with periodic removal of acid sludge material that collects therein. The hydrocarbon phase is then passed via line 8 to fractionation system 9.

Fractionation system 9 rst separates unreacted benzene from the mixture of hydrocarbon charged thereto. The separated benzene fraction is then recycled via line 12 to the alkylation zone. The bottoms from the benzene column are passed to an alumina treating zone wherein alkyl uorides are removed, and the resulting alkyl fluoride free hydrocarbon mixture is further separated into: a normal paran-containing fraction, which is recycled via line 14 to dehydrogenation zone 30, a phenyl-substituted normal paraffin fraction which is recovered via line 10, and a heavy alkylate fraction which leaves the process via line 11.

The composition of non-normal hydrocarbons in the recycle paraffin stream passing through line 14 and the weight percent of the detergent alkylate recovered via line 10 that is phenyl-substituted normal parain hydrocarbon are monitored as a function of time on stream measured in barrels of combined charge per pound of catalyst in dehydrogenation zone 20. Results of this run are shown in Table I.

TABLE 1.-RESULTS OF CONTROL RUN Wt. percent of phenyl-substi- Wt. percent tuted normal non-normal in paraliins in line 14 detergent alkylate Time On Stream bbL/lb.

From the table, it can be seen that the fall in quality of the detergent alkylate was paralleled by a rise in the weight percent of non-normal in line 14. Likewise, temperature levels necessary to sustain the desired conversion levels changed relatively rapidly during this run indicating a progressive deactivation of the catalyst.

A second run is then made with a fresh batch of dehydrogenation catalyst in the same manner as above except this run is made with lines 15 and 18 open, thereby including separating system 16 in the process. Separating system 16 in this case consists of two columns containing pelleted calcium aluminosilicates which selectively extract normal para'ins. These two columns are operated in swing-bed fashion with one being on a n-parafn recovery cycle while the other is on an extraction cycle. According to the present invention, a sidestream, amounting to about 2.5% of normal paraffin recycle stream flowing through line 14, is withdrawn therefrom and passed via line 15 to separating system 16. Assuming that separating system 16 is just starting a new cycle, the sidestream is passed to the` column beginning the extraction portion of the cycle. This stream flows downwardly through the column, at a temperature of about 70 F., and a normal paraffinfree stream is Withdrawn from the bottom of the column and passed via line 17 out of the process. Turning now to the column that is on the recovery portion of the cycle, it is being contacted with a normal pentane stream in downtlow fashion. This normal pentane stream displaces the extracted C11 to C14 normal parans and the eflluent from the bottom of this column is passed to a distillation column wherein a minor amount of n-pentane is taken overhead and a substantially pure normal parafiin fraction recovered as bottoms. This last fraction is then passed out of separating system 16 by line 18 and back into line 14. The stream flowing through line 18 is 98.5 wt. percent pure C11-C14 n-parain. The necessary piping and valving to effect reversal of the two columns in separating system 16 are well-known and are not considered here.

In this second run, the concentration of non-normal parains in recycle stream 14 at the point it joins line 14 is maintained constant at about 3.2% by the use of separatmg system 16 as outlined above. Moreover, the quallty of the detergent alkylate being recovered via line 10 1s ma1ntained constant at about 98% by weight phenylsubst1tuted normal parain hydrocarbons. Lastly, the rate of temperature increase necessary to sustain a conversion level of 10% in dehydrogenation zone 20 is a factor of 2 less in this second run than in the rst run.

I claim as my invention:

l.. In a process for the preparation of an aryl-substituted normal parain hydrocarbon wherein:

(a) a normal paraffin hydrocarbon and hydrogen are contacted with a dehydrogenation catalyst in a first conversion zone at conditions suicient to form a normal mono-olefin having the same number of carbon atoms as the normal parain hydrocarbon with attendant formation of non-normal hydrocarbons;

(b) a mixture of hydrogen and hydrocarbons is withdrawn from the lirst conversion zone and separated into a hydrogen-rich gaseous phase and a hydrocarbon-rich liquid phase;

(c) the hydrocarbon-rich liquid phase and a monocyclic aromatic hydrocarbon are contacted in a second conversion zone with an alkylation catalyst at conditions suicient to form arylalkyl compounds;

' (d) a mixture of hydrocarbons is Withdrawn from the second conversion zone and separated into a monocyclic-aromatic-rich fraction, a normal paran-rich fraction containing non-normal hydrocarbons, and an aryl-substituted normal parafn fraction;

(e) the normal parafn-fraction is recycled t the rst conversion zone; and,

(f) the non-normal hydrocarbons contained in the normal parain-rich fraction cause deactivation of the dehydrogenation catalyst and deterioration in the quality of the aryl-substituted normal paraiiin-containing fraction;

the improvement comprising removing non-normal hydrocarbons from at least a portion of the recycled normal parafn-rich fraction, thereby increasing the stability of the dehydrogenation catalyst and improving the' quality of the aryl-substituted normal parain hydrocarbon fraction.

2. The improved process of claim 1 further characterized in that said normal parain hydrocarbon contains 9 to about 20 carbon atoms.

3. The improved process of claim 1 further characterized in that said mono-cyclic aromatic is selected from the group consisting of benzene, toluene, Xylene, ethyl benzene, methylethyl benzene, phenol, diethyl benzene and mono-nitro benzene.

4. The improved process of claim 1 further characterized in that said dehydrogenation catalyst comprises: an alumina component; a component selected from the group consisting of alkali metals, alkaline earth metals and compounds thereof; a component selected from the group consisting of arsenic, bismuth, antimony, sulfur, selenium, tellurium, and compounds thereof; and a platinum group metallic component.

5. The improved process of claim 1 further characterized in that alkylation catalyst is hydrogen fluoride.

6. The improved process of claim 1 further characterized in that said dehydrogenation catalyst comprise's alumina, about 0.01% to about 1.5 by weight of lithium, about 0.05% to about 5.10% by weight of a platinum and about 0.01% to about 1% by weight of arsenic.

7. The improved process of claim 1 further characterized in that said monocyclic aromatic is benzene and that said normal paraffin hydrocarbon contains 9 to l5 carbon atoms.

8.v The improved process of claim 1 further characterized in that the normal parain hydrocarbon charged thereto is obtained by separating it from a hydrocarbon charge stock containing both normal and non-normal hydrocarbons in a separating system employing a bed of molecular sieves, and further in that the removal of nonnormal hydrocarbons from at least a portion of the recycled normal parain-rich fraction is effected by cornmingling said fraction with the charge stock to said separating system.

9. The improved process of claim 8 further characterized in that said molecular sieves comprise an alkali metal aluminosilicate containing pores of about 5 angstrom units in diameter.

References Cited UNITED STATES PATENTS 3,169,987 2/1965 Bloch 260-671 XR 2,887,518 5/1959 Bloch et al. 260-671 3,349,144 10/1967 Alul et al 260-671 3,312,734 4/1967 Jones 260--671 XR DELBERT E. GANTZ, Primary Examiner CURTIS R. DAVIS, Assistant Examiner 

